[llvm-commits] [llvm] r71168 - in /llvm/trunk: lib/Analysis/CaptureTracking.cpp test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll
Duncan Sands
baldrick at free.fr
Thu May 7 11:08:34 PDT 2009
Author: baldrick
Date: Thu May 7 13:08:34 2009
New Revision: 71168
URL: http://llvm.org/viewvc/llvm-project?rev=71168&view=rev
Log:
Revert r70876 and add a testcase (@c7) showing the problem:
bits captured, but the pointer marked nocapture. In fact
I now recall that this problem is why only readnone functions
returning void were considered before! However keep a small
fix that was also in r70876: a readnone function returning
void can result in bits being captured if it unwinds, so
test for this.
Modified:
llvm/trunk/lib/Analysis/CaptureTracking.cpp
llvm/trunk/test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll
Modified: llvm/trunk/lib/Analysis/CaptureTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/CaptureTracking.cpp?rev=71168&r1=71167&r2=71168&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/CaptureTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/CaptureTracking.cpp Thu May 7 13:08:34 2009
@@ -49,7 +49,13 @@
switch (I->getOpcode()) {
case Instruction::Call:
case Instruction::Invoke: {
- CallSite CS(I);
+ CallSite CS = CallSite::get(I);
+ // Not captured if the callee is readonly, doesn't return a copy through
+ // its return value and doesn't unwind (a readonly function can leak bits
+ // by throwing an exception or not depending on the input value).
+ if (CS.onlyReadsMemory() && CS.doesNotThrow() &&
+ I->getType() == Type::VoidTy)
+ break;
// Not captured if only passed via 'nocapture' arguments. Note that
// calling a function pointer does not in itself cause the pointer to
@@ -58,69 +64,46 @@
// that loading a value from a pointer does not cause the pointer to be
// captured, even though the loaded value might be the pointer itself
// (think of self-referential objects).
- bool MayBeCaptured = false;
CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
for (CallSite::arg_iterator A = B; A != E; ++A)
- if (A->get() == V && !CS.paramHasAttr(A-B+1, Attribute::NoCapture)) {
- // The parameter is not marked 'nocapture' - handled by generic code
- // below.
- MayBeCaptured = true;
- break;
- }
- if (!MayBeCaptured)
- // Only passed via 'nocapture' arguments, or is the called function -
- // not captured.
- continue;
- if (!CS.doesNotThrow())
- // Even a readonly function can leak bits by throwing an exception or
- // not depending on the input value.
- return true;
- // Fall through to the generic code.
+ if (A->get() == V && !CS.paramHasAttr(A - B + 1, Attribute::NoCapture))
+ // The parameter is not marked 'nocapture' - captured.
+ return true;
+ // Only passed via 'nocapture' arguments, or is the called function - not
+ // captured.
break;
}
case Instruction::Free:
// Freeing a pointer does not cause it to be captured.
- continue;
+ break;
case Instruction::Load:
// Loading from a pointer does not cause it to be captured.
- continue;
+ break;
case Instruction::Ret:
if (ReturnCaptures)
return true;
- continue;
+ break;
case Instruction::Store:
if (V == I->getOperand(0))
// Stored the pointer - it may be captured.
return true;
// Storing to the pointee does not cause the pointer to be captured.
- continue;
- }
-
- // If it may write to memory and isn't one of the special cases above,
- // be conservative and assume the pointer is captured.
- if (I->mayWriteToMemory())
- return true;
-
- // If the instruction doesn't write memory, it can only capture by
- // having its own value depend on the input value.
- const Type* Ty = I->getType();
- if (Ty == Type::VoidTy)
- // The value of an instruction can't be a copy if it can't contain any
- // information.
- continue;
- if (!isa<PointerType>(Ty))
- // At the moment, we don't track non-pointer values, so be conservative
- // and assume the pointer is captured.
- // FIXME: Track these too. This would need to be done very carefully as
- // it is easy to leak bits via control flow if integer values are allowed.
+ break;
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::PHI:
+ case Instruction::Select:
+ // The original value is not captured via this if the new value isn't.
+ for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE; ++UI) {
+ Use *U = &UI.getUse();
+ if (Visited.insert(U))
+ Worklist.push_back(U);
+ }
+ break;
+ default:
+ // Something else - be conservative and say it is captured.
return true;
-
- // The original value is not captured via this if the new value isn't.
- for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI) {
- Use *U = &UI.getUse();
- if (Visited.insert(U))
- Worklist.push_back(U);
}
}
Modified: llvm/trunk/test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll?rev=71168&r1=71167&r2=71168&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll (original)
+++ llvm/trunk/test/Transforms/FunctionAttrs/2008-12-31-NoCapture.ll Thu May 7 13:08:34 2009
@@ -49,6 +49,21 @@
ret i1 1
}
+define i1* @lookup_bit(i32* %q, i32 %bitno) readnone nounwind {
+ %tmp = ptrtoint i32* %q to i32
+ %tmp2 = lshr i32 %tmp, %bitno
+ %bit = and i32 %tmp2, 1
+ %lookup = getelementptr [2 x i1]* @lookup_table, i32 0, i32 %bit
+ ret i1* %lookup
+}
+
+define i1 @c7(i32* %q, i32 %bitno) {
+ %ptr = call i1* @lookup_bit(i32* %q, i32 %bitno)
+ %val = load i1* %ptr
+ ret i1 %val
+}
+
+
define i32 @nc1(i32* %q, i32* %p, i1 %b) {
e:
br label %l
@@ -79,14 +94,8 @@
ret void
}
-define void @nc5(void (i8*)* %p, i8* %r) {
- call void %p(i8* %r)
- call void %p(i8* nocapture %r)
- ret void
-}
-
-declare i8* @external_identity(i8*) readonly nounwind
-define void @nc6(i8* %p) {
- call i8* @external_identity(i8* %p)
+define void @nc5(void (i8*)* %f, i8* %p) {
+ call void %f(i8* %p) readonly nounwind
+ call void %f(i8* nocapture %p)
ret void
}
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